An integrated circuit package generally includes an integrated circuit having an active face lying on a chip support pad connected to a leadframe and encapsulated by a material. Plastic is one example of an encapsulating material. The IC package is typically mounted to a printed circuit board. Reflow solder is one technique used to surface mount the IC package to a printed circuit board.
As the industry moves towards higher circuit densities and larger memory sizes, more stringent requirements are being placed on low frequency noise suppression (also known as power line de-coupling) and noise filtering systems on printed circuit boards. De-coupling, or bypass, capacitors are necessary to provide a temporary supply of charge to the integrated circuits as the output of power supplies connected to the integrated circuits varies. In this way, circuit operation is not compromised due to a temporary drop in voltage supply. To enhance de-coupling, these bypass capacitors need to be as close to the devices as possible in order for the inductance between the capacitors and the devices to be as small as possible.
Integrated circuits of higher densities and larger memory sizes have thinner di-electrics between their internal interconnect levels. As such, these circuits are much more susceptible to damage from noise spikes on power lines of the power supplies.
Designers of integrated circuit packages have chosen between including a low frequency noise suppression device or a high frequency noise suppression device with the IC package. This restriction exists as only one capacitor can be encapsulated with the integrated circuit chip in a single package. The difficulity in adding multiple capacitors in a package arises from the design of the conventional leadframe where the power supply pins and busses (Vss and Vdd) are spaced physically far apart from each other. This requires long interconnects or a long capacitor for electrically connecting the electrodes of the capacitor and the respective power pins. As frequency handling charecteristics differ for different capacitors, a single capacitor cannot handle both low end frequency and high end frequency noise noise suppression. Additionally, a long capacitor body can cause undue stresses on plastic encapsulated packages because of the different thermal expansion coefficients between the plastic encapsulant and the ceramic capacitor body. This causes package reliability problems. Concurrent over voltage spike protection has also not been possible.
FIG. 1a is a cross section view of a typical prior art IC device package 10. IC device package 10 is illustrated in the conventional plastic small outline J-leaded (PSOJ) surface mount package. A semiconductor die 11 is positioned by an epoxy 12a to a mount support pad 12b of leadframe 13. Wirebonds 14 are connected near the outer edges of semiconductor die 11 bonding semiconductor die 11 to leadfingers 15. An encapsulating material 16, plastic for example, surrounds semiconductor die 11, mount support pad 12b, leadframe 13, wirebonds 14, and parts of leadfingers 15 so that IC device package 10 can be surface mounted to a printed circuit board, not shown. A reflow solder process can be used to surface mount IC device package 10 to a printed circuit board.
FIG. 1b is a partial inside top view of prior art IC device package 10. In addition to leadframe 13, mount support pad 12b, and semiconductor die 11, illustrated are power supply busses 16 and 17. Power supply bus 16 delivers Vss and power supply bus 17 delivers Vdd. Power supply busses 16 and 17 are not adjacent to each other, but are spaced physically apart and are not near each other. If IC package device 10 contained a de-coupling capacitor for low frequency noise suppression, it would lie underneath mount pad 12 and be a long terminal device having its electrodes connected between Vss and Vdd. The de-coupling capacitor would necessarily be a long terminal device because power supply busses 16 and 17 are not adjacent to each other. Such a capacitor is illustrated in FIG. 1b as capacitor 19.
FIG. 2 is a partial cross section view of an alternative prior art IC device 10a having a de-coupling capacitor 19a conected across power supply lead 16a that supplies Vss and power supply lead 17a that supplies Vdd. Power supply leads 16a and and 17a are not adjacent to each other, but are across from each other. Decoupling capacitor 19a acts as the mount support pad to support semiconductor die 11a. The addition of an encapsulating substance, not shown, such as plastic would surround alternative IC device 10a to form an IC device package that can be mounted to a printed circuit board.
In the prior art devices of FIGS. 1a through 2, only a single electronic device can be connected to the power supply leads Vss and Vdd. The de-coupling capacitor has been illustrated. The designer could have chosen a high frequency noise suppression capacitor instead of the de-coupling capacitor. However, both a de-coupling capacitor and a high frequency noise suppression capacitor cannot be incorporated into the package device of FIGS. 1a through 2. The physical size of the capacitors, long bodies and electrodes, makes it not possible to encapsulate more than one in the package.
It is an object of this invention to provide an integrated circuit package device that has both low end frequency and high end frequency noise suppression.
It is a further object of this invention to provide an integrated circuit package device that has over voltage protection.
Other objects and benefits of this invention will be apparent to those skilled in the art based upon the description to follow herein.